WO2001088044A1

WO2001088044A1 - Pigments

Info

Publication number: WO2001088044A1
Application number: PCT/EP2001/004630
Authority: WO
Inventors: Ralf Anselmann; Thomas Albrecht; Sara Rodriguez-Mozaz
Original assignee: Merck Patent Gmbh
Priority date: 2000-05-18
Filing date: 2001-04-25
Publication date: 2001-11-22
Also published as: US6818051B2; CN1232589C; EP1285031A1; DE10024466A1; AU2001256320A1; KR20030005351A; CA2408990A1; JP2003533579A; US20030116062A1; CN1443223A

Abstract

The invention relates to particles having an opalescent effect. The size of said particles ranges from 5 νm to 5000 νm. The particles consist of monodisperse globules having a diameter of 50 nm - 2 νm, the standard deviation being less than 5 % in a regularly arranged, three-dimensional densely packed structure according to domain. Said structure is mechanically stabilized by physical or chemical modification.

Description

pigments

The invention relates to pigments, in particular interference pigments, which are characterized by a three-dimensional, periodic arrangement of monodisperse spheres in the nanometer range.

Natural precious opals consist of monodisperse, regularly arranged silica gel spheres with diameters of 150-400 nm. The play of colors of these opals comes about through Bragg-like scattering of the incident light on the lattice planes of the crystal-like spheres.

There has been no shortage of attempts to synthesize white and black opals for jewelry purposes, using water glass or silicone esters as the starting product.

US 4 703 020 describes a method for producing a decorative material which consists of amorphous silica spheres which are arranged three-dimensionally, zirconium oxide or zirconium hydroxide being located in the spaces between the spheres. The beads have a diameter of 150-400 nm. The production takes place in two stages. In a first stage, silica spheres are sedimented from an aqueous suspension. The mass obtained is then dried in air and then calcined at 800 ° C.

In a second stage, the calcined material is introduced into the solution of a zirconium alkoxide, the alkoxide penetrating into the spaces between the balls and zirconium oxide being precipitated by hydrolysis. This material is then calcined at 1000-1300 ° C. In contrast to a natural opal, the material obtained has zirconium dioxide in the cavities between the individual spheres.

The mechanical stabilization of the material takes place once through the inclusion of the zirconium oxide and very significantly also through the

Calcination, which is known to change the physical and chemical structure of the material. The manufacturing process described here has the disadvantage that it has to be calcined several times at high temperatures. It is therefore very energy intensive.

The object of the present invention was to achieve the above-mentioned. To avoid disadvantages. In particular, a particulate material should be made available that shows opalescent effects comparable to natural opal and at the same time has sufficient mechanical stability. Another object of the invention was to provide a manufacturing process for such a material which allows defined particles with optimized energy expenditure to be obtained which can be used as pigments.

A first object of the present invention are therefore particles with an opalescent effect, which have a particle size in the range from 5 μm to 5000 μm, wherein the particles consist of monodisperse spheres with a diameter of 50 nm - 2 μm with a standard deviation of less than 5% in a three-dimensional, domain-densely packed and regularly arranged structure, which is mechanically stabilized by a physical or chemical modification.

Another object of the present invention is a method for producing particles in which in one step a) monodisperse spheres with a diameter of 50 nm to 2 μm with a standard deviation of less than 5% are suspended in a liquid medium,

b) the suspension is applied to a surface,

c) the liquid medium is removed.

The invention furthermore relates to the use of the particles according to the invention as pigments, in particular in paints, lacquers, n

Printing inks, plastics, ceramic materials, glasses and cosmetic formulations. For this you can also use commercially available pigments, for example inorganic and organic absorption pigments, metallic effect pigments and LCP

Pigments. Furthermore, the invention

• I C

^ Particles also for the production of pigment preparations as well as for the production of dry preparations, e.g. Suitable for granules.

The three-dimensionally packed and regularly arranged structure is particularly important for achieving the opalescent effect in the particles according to the invention. This three-dimensionally packed and regularly arranged structure is usually not a perfect order that extends across the entire particle. To achieve the desired color effects, it is sufficient if the particles according to the invention have individual domains within which there is a uniform arrangement. To explain this structure, FIGS. 1 and 2 can be used in particular, which show exactly the presence of ordered domains made of monodisperse spheres and at the same time show that there is in no way a dense or even densest spherical packing for the entire particle. The physical or chemical modification for mechanical stabilization is also essential for the particles according to the invention with an opalescent effect, since without such stabilization the particles would not be fixed in their spatial shape. However, the modification must not take place in any mechanically stabilizing manner, since otherwise the opalescent effect, as already described above, would be impaired. The difference in refractive index between the spheres and the material in the spaces significantly influences the optical properties of the particles. Therefore, such physical or chemical modifications are preferred that make it possible to maintain a corresponding refractive index difference. In principle, the effects according to the invention can be observed with refractive index differences in the range from approximately 0.01 to approximately 2. The optimal refractive index difference for opalescent pigments is in the range of about 0.1 to 0.6, but significantly smaller or larger refractive index differences are also suitable to show opalescent effects. With small refractive index differences such as about 0.01 to about 0.02, the particles are largely transparent and therefore have particularly pronounced opalescent effects due to the many effective reflection levels. However, the intensity of these effects is only weak due to the transparency.

The monodisperse spheres used, including any coatings that may be present, have a diameter in the range from 50 nm to 2 μm, spheres with a diameter of 150-1500 nm preferably being used. Spheres in the range from 200 to 500 nm are particularly preferably used, since in the case of particles in this order of magnitude the reflections of different wavelengths of visible light differ significantly from one another, and so the opalescence occurs particularly distinctly in a wide variety of colors. In a variant of the present invention, however, it is also preferred to use multiples of this preferred particle size, which then increase Reflections corresponding to the higher orders and thus lead to a wide play of colors.

The monodisperse spheres can consist of almost any materials that are suitable for the wavelengths

Reflections of light are sufficiently transparent that this light can penetrate several spherical diameters deep into the particle. Preferred spheres consist of metal chalcogenides, preferably metal oxides or metal pnictides, preferably nitrides or phosphides. Metal in the sense of these terms are all elements that can appear as electropositive partners in comparison to the counterions, such as the classic metals of the subgroups or the main group metals of the first and second main group, but also all elements of the third main group as well as silicon, germanium, tin , Lead, phosphorus, arsenic, antimony and bismuth. The preferred metal chalcogenides and metal pnictides include in particular silicon dioxide, aluminum oxide, titanium dioxide, zirconium dioxide, gallium nitride, boron and aluminum nitride as well as silicon and phosphorus nitride.

Monodisperse spheres made of silicon dioxide are preferably used as the starting material for the production of the particles according to the invention and can be obtained, for example, by the process described in US Pat. No. 4,911,903. The spheres are produced by hydrolytic polycondensation of tetraalkoxysilanes in an aqueous-ammoniacal medium, first of all producing a sol of primary particles and then bringing the SiO ₂ particles obtained to the desired particle size by continuous, controlled metering in of tetraalkoxysilane. This method can be used to produce monodisperse SiO ₂ spheres with average particle diameters between 0.05 and 10 μm with a standard deviation of 5%. SiO ₂ balls which are coated with non-absorbent metal oxides, such as TiO ₂ , ZrO ₂ , ZnO ₂ , SnO ₂ or Al ₂ O ₃ , are also preferred as the starting material. The production of SiO ₂ balls coated with metal oxides is described in more detail, for example, in US Pat. No. 5,846,310, DE 198 42 134 and DE 199 29 109. Coating with absorbent metal oxides, such as the iron oxides Fe ₃ O or Fe ₂ O ₃ , also leads to particles which can be used according to the invention.

Monodisperse balls made of non-absorbent metal oxides such as TiO ₂ , ZrO ₂ , ZnO ₂ , SnO ₂ or Al ₂ O ₃ or metal oxide mixtures can also be used as the starting material. Their manufacture is described for example in EP 0 644 914. Furthermore, the method according to EP 0 216 278 for the production of monodisperse SiO ₂ spheres can be transferred to other oxides easily and with the same result. Tetraethoxysilane, tetrabutoxytitanium, tetrapropoxyzirconium or their mixtures are added in one pour with vigorous mixing to a mixture of alcohol, water and ammonia, the temperature of which is adjusted with a thermostat to between 30 and 40 ° C., and the mixture obtained for a further 20 Vigorously stirred for seconds, forming a suspension of monodisperse spheres in the nanometer range. After a post-reaction time of 1 to 2 hours, the balls are separated off, washed and dried in the customary manner, for example by centrifugation.

Monodisperse polymer balls, for example polystyrene or polymethyl methacrylate, can also be used as the starting material for the production of the particles according to the invention. Such balls are commercially available. Bangs Laboratories Inc. (Carmel, USA) offer monodisperse spheres made from a wide variety of polymers.

Furthermore, monodisperse spheres of polymers are also used as the starting material for the production of the pigments according to the invention suitable that contain particles, for example metal oxides, included. Such materials are offered by the company micro caps Entwicklungs- und Vertriebs GmbH in Rostock. According to customer-specific requirements, microencapsulations based on polyester, polyamides and natural and modified

Carbohydrates.

Monodisperse balls made of metal oxides, which are coated with organic materials, for example silanes, can also be used. The monodisperse spheres are dispersed in alcohols and modified with common organoalkoxysilanes. The silanization of spherical oxide particles is also described in DE 43 16 814.

The pigment particles produced from the monodisperse spheres with an average particle size of 5 μm - 5 mm preferably have a platelet-shaped structure.

Such a platelet-shaped particle is shown in FIG. 1. In another preferred embodiment of the present invention, the particles have an almost spherical three-dimensional shape, as shown in FIG. 2. Here, too, the average particle size is usually in the range from 5 μm to 5 mm. this embodiment has the advantage that the pigments have no preferred direction. Therefore, for example, when processing in plastic injection molding, there are no streaks due to the preferred orientations of the pigments in the matrix.

The pigments according to the invention can be prepared by 2 alternative processes. In the droplet process, the monodisperse spheres are preferably suspended in a liquid medium in a concentration of 1-35% by weight. The suspension is sprayed so that drops form on a surface. The liquid medium is then removed, preferably by drying under mild conditions, in such a way that the balls partially arrange themselves.

It is essential that the suspension is sprayed on a smooth surface in such a way that individual drops form that do not run together. The wettability of the surface by the dispersant used is essential for the shape of the particles formed. If the wetting tension is positive, i. H. the contact angle (for a definition of the contact angle, see e.g. Dörfler, interfaces and colloid chemistry, VCR 1994, page 34) is less than 90 °, it is said that the surface is wetted by the liquid. In this case, the beads in the drop are transported to the edge of the drop by capillary forces, so that preferably ring-like structures are formed which are difficult to use as pigment particles. In order to form preferred, compact, plate-like, lenticular or even spherical particles according to the invention, however, the surface should not be wetted or only incompletely, i.e. the wetting tension is negative, ie the contact angle is greater than 90 ° (cf. FIGS. 1 and 2). The exact shape of the particles is also affected by the concentration of the suspension, the initial drop diameter, the speed of drying and the interaction between the suspended beads and the surface.

After the removal of the liquid medium in step c), the particles are then detached from the surface in a subsequent step d) in a dry or wet manner.

If the surface is smooth, particles with a preferred orientation are formed in which the same reflection planes are simultaneously in the reflection position. In this way, particularly intense reflections can be achieved. Therefore, in a preferred embodiment according to the invention, the surface is a smooth surface. Particularly good quality particles can be obtained if the droplets are applied monodisperse. Easily evaporable solvents, for example alcohols, lower alkanes, mixtures of organic solvents and water and solvent-water mixtures, can be used as dispersants for the dispersion of the monodisperse spheres.

The preferably smooth surface onto which the droplets are sprayed can be made of glass, metal or plastic. An endless belt made of a thermally stable plastic or a metal, in particular stainless steel, is particularly suitable. Suitable plastic materials are polyethylene terephthalate, other polyesters, polyacrylates and in particular polytetrafluoroethylene.

Modified inkjet printers, for example, can be used as the spraying device. The drops sprayed onto the surface are dimensioned according to the use of the pigment.

Drying of the droplets can be accelerated by applying heat. If an endless belt is used, it is guided with the sprayed-on drops through a drying section, which can consist of one or more sections. A preferred embodiment of the drying zone has a drying device in which drying is carried out with an IR drying device.

The individual particles formed, which are shown in FIG. 1 or FIG. 2 (image taken with the aid of a scanning electron microscope), can be separated from the smooth surface by a device. The separation can take place either mechanically by scraping or brushing or without contact by dissolving a “release layer” or by ultrasound respectively. Separation with a liquid or gas jet has proven to be advantageous.

An alternative method for producing the pigments with an opal structure according to the invention is a continuous coil coating. A

Suspension of the monodisperse spheres is not sprayed into individual drops, but is deposited on a carrier as a liquid film and, after sedimentation, drying and solidification, is reduced to platelets of a suitable size. EP 0 608 388 describes the production of platelet-shaped pigments using a continuous belt process.

The method according to the invention, in particular in this embodiment, can also be used for coating, in particular for painting surfaces. Therefore, this use is also the subject of the present invention.

The endless belt, which is passed over a roller system, passes through a task line, where it is coated with a thin film of the dispersion of the monodisperse balls in a solvent or water. The dispersion is applied according to known methods via a roller system or a nozzle. This nozzle can be designed as a single-substance or multi-substance nozzle. In addition, a variable diaphragm or an airbrush ("air brush") in which a sharp air jet is blown through a slot nozzle can be arranged to adjust the layer thickness of the applied film.

The coated strip is then also passed through a drying section. The layer formed is then separated from the belt by a device. The separation can take place either mechanically by scraping or brushing or without contact by dissolving a “release layer” or by ultrasound The separation with a liquid or gas jet has proven to be advantageous.

It is advisable to mechanically stabilize the particles before detaching them from the surface in order to solidify the opal structure so that the necessary mechanical stability of the pigment particles is ensured. Stabilization can be achieved by the following physical and chemical measures.

The surface of the balls is modified in order to achieve crosslinking of the balls or better adhesion of the balls to one another during the formation of the opal structure. To suspend the spheres in a liquid medium, a compound which can be hydrolyzed in water can preferably be added, the hydrolysis product of which precipitates on the spheres during the formation of the opal structure and brings about a chemical bond between the spheres. In the case of spheres made of silicon dioxide, tetraethyl orthosilicate is preferably added to the suspension at temperatures of 50 to 80 ° C., which hydrolyzes to silicon dioxide and leads to a chemical bond between the spheres. Alternatively, silicon tetrachloride can also be used to treat the coated surface.

The particles according to the invention can also be chemically stabilized by adding soluble silicates, for example sodium water glass and / or polymerizable soluble aluminum compounds in the suspension.

Stabilization can also be achieved by treating the coated surface with soluble silicates. The particles can also be physically stabilized by being embedded in transparent plastics or suitable paints. It is essential for the embedding material that it is transparent and one has a suitable refractive index, which leads to an optimal refractive index difference. For easy processing of the embedding material, for example a varnish, it is particularly advantageous if it is low-viscosity and its volume does not change, or changes only very little, during curing. In one possible

Embodiment, the embedding material or its precursor is already contained in the suspension in a corresponding volume fraction.

In a further embodiment of the solidification of the opal structure, the surface of the spheres is modified with silanes, which are then crosslinked with one another by heat or UV radiation during the formation of the opal structure. This networking also leads to a solidification of the opal structure. The silanization of monodisperse silicon dioxide balls is described in more detail in DE 43 16 814.

The pigment according to the invention can be used for pigmenting paints, powder coatings, paints, printing inks, plastics and cosmetic formulations, such as e.g. lipsticks, nail polishes, cosmetic sticks, press powder, make-ups, shampoos and loose powders and gels.

The concentration of the pigment in the application system to be pigmented is generally between 0.1 and 70% by weight, preferably between 0.1 and 50% by weight and in particular between 1.0 and 20% by weight, based on the Total solid content of the system. It is usually dependent on the specific application.

Plastics usually contain the pigment according to the invention in amounts of from 0.01 to 50% by weight, preferably from 0.01 to 25% by weight, in particular from 0.1 to 7% by weight, based on the plastic composition. In the paint sector, the pigment mixture is used in amounts of 0.1 to 30% by weight, preferably 1 to 10% by weight, based on the paint dispersion.

When pigmenting binder systems e.g. for colors and

Printing inks for gravure printing, offset printing or screen printing, or as a preliminary product for printing inks, for example in the form of highly pigmented pastes, granules, pellets, etc., have in particular pigment mixtures with spherical colorants, such as TiO ₂ , carbon black, chromium oxide, iron oxide and organic “ Color pigments ", have proven to be particularly suitable. The pigment is generally incorporated into the printing ink in amounts of 2-35% by weight, preferably 5-25% by weight, and in particular 8-20% by weight. Offset printing inks can the pigment contains up to 40% by weight and more The precursors for the printing inks, for example in granular form, as pellets, briquettes, etc., contain up to 95% by weight of the pigment according to the invention in addition to the binder and additives Formulations which contain the pigment according to the invention are therefore also an invention.

The following examples are intended to explain the invention in more detail without limiting it.

example 1

0.29 g of monodisperse SiO ₂ spheres with a diameter of 250 nm are dispersed in 50 ml of ethanol and 19 ml of fully demineralized water and 12 ml of 25% ammonia are added to this dispersion. The suspension is heated to 70 ° C. with vigorous stirring and 0.2 ml of tetraethyl orthosilicate is added dropwise. The suspension is placed in a petri dish and the liquid phase is allowed to evaporate at 70 ° C. A white powder is obtained by scraping off the residue with an opalescent effect, whereby the perceived reflection color is angle-dependent.

Example 2 The suspension prepared according to Example 1 is added after the

Tetraethyl orthosilicate cooled to 23 ° C sprayed on an airbrush (air brush) onto a hydrophobic silicon wafer. The drops are allowed to dry in a stream of argon at 23 ° C. The residue is rinsed off the substrate with water, separated off via a filter and dried at 110 ° C.

Example 3

An aqueous suspension (16% by weight) of monodisperse SiO ₂ spheres with a diameter of 250 nm is sprayed at 23 ° C. over an airbrush onto a Teflon surface. The drops are allowed to dry. The coated Teflon surface is then transferred to a sealed vessel in which there is an atmosphere of argon and silicon tetrachloride. After a short exposure time, a residue treated in this way is rinsed off with water from the Teflon surface, separated off via a filter and dried at 110 ° C.

Claims

claims

1. Particles with an opalescent effect, which have a particle size in the range from 5 μm to 5000 μm, consisting of monodisperse spheres with a diameter of 50 nm to 2 μm with a standard deviation of less than 5% in a domain-wise three-dimensional, densely packed and regular arranged structure, which is mechanically stabilized by a physical or chemical modification.

2. Particles according to claim 1, wherein the monodisperse spheres are transparent and consist of metal chalcogenide or metal pnictide and are optionally additionally coated with preferably non-absorbent metal chalcogenide, metal pnictide or organic polymer.

3. Particle according to claim 1, wherein the monodisperse spheres consist of a polymer.

4. Particles according to claim 1 or 2, wherein the monodisperse spheres consist of a metal oxide, preferably silicon dioxide, and the surface thereof, preferably with at least one silane, is modified.

5. Use of particles according to at least one of claims 1 to 4 as a pigment.

6. Use of particles according to at least one of claims 1 to 4 for pigmenting lacquers, powder coatings, paints, printing inks, plastics or cosmetic formulations.

Process for the production of particles by a) suspending monodisperse spheres with a diameter of 50 nm to 2 μm with a standard deviation of less than 5% in a liquid medium, b) applying the suspension to a surface, c) removing the liquid medium.

8. Use of the method according to claim 7 for coating (painting) of surfaces.

9. The method according to claim 7, characterized in that the particles in a step d) are detached from the surface in a dry or wet way.

10. The method according to at least one of claims 7 or 9, characterized in that the structure formed is stabilized physically or chemically in step d).

11. The method according to at least one of claims 7 or 9 to 10, wherein the surface of the balls is modified chemically, preferably with at least one silane.

12. The method according to at least one of claims 7 or 9 to 10, wherein to the suspension of the balls a water hydrolyzable compound, preferably an alkoxide and particularly preferably

Tetraethoxysilicate, is added.

13. The method according to at least one of claims 7 or 9 to 12, wherein the spaces between the balls are subsequently filled with a material that is a suitable

Has refractive index.